Flexible electric heater for deicing airfoils



Feb. 7, 1950 R. s. ELY ET AL 2,496,279

FLEXIBLE ELECTRIC HEATER FOR DE-ICING AIR FOILS Feb. 7, 1956 R. s. ELYET AL. 2,496,279

RLEXIBLRELECTRIC HEATER RoR DE-ICING AIR Fons Filed Feb. l0, 1945 2Sheees-SheeftI 2 INVENTORS ROer'/SZEZ fi/@asses BY Patented Feb. 7, 1950FLEXIBLE ELECTRIC HEATER FOR DEICING AIRFOILS Robert S. Eiy, Westbury,and Irving M. Ketcham,

Roslyn Heights, N. Y., assignors, by mesne assignments, to Safeway HeatElements, Inc., New York, N. Y., a corporation of Delaware ApplicationFebruary 10, 1945, Serial No. 577,232

3 Claims.

One object of the invention is to provide a heater which will emitdifferent amounts of heat per unit of surface from different areas ofthe heater. A further object of the invention is to provide a heaterwhich is flexible enough to be cemented or otherwise aixed in heat eX- jchange relationship to curved or uneven surfaces.

Devices in use for de-icing of the pulsating boot type are heavy,expensive to maintain and uncertain in their function. The resistor typeheaters used heretofore, for this purpose emit uniform amounts of heatfrom all parts of their surface Whereas it has been found that greaterconcentrations of heat are demanded in some areas and less heat inothers.

In our invention these objects to construction of the prior art areovercome by providing a heater which is Woven in the formr of a flexibleblanket or tape in which different concentrations of heat are emitted atvarious parts of the heater so that when it is used for de-icing thegreatest amount of heat will be given olf at the places Where ice formsthe fastest. In the Vpreferred embodiment of the invention the heaterfabric consists of flexible resistor Wires forming the warp and the Woofis Woven with thread made from glass, asbestos or other heat resistingdielectric material. In some cases We may use resistor wire in both thewarp and the Woof of the fabric. In this case the warp or Woof wires orboth would be insulated with a heat resisting dielectric such as braidedglass or asbestos sleeving. We may also use some dielectric threads inthe warp to reinforce the fabric at the edges and between the groups ofWires.

In the preferred form the diierent heat concentrations are achieved byserially connecting warp Wires of different resistance or by seriallyconnecting groups of warp wires of different resistance. In a seriescircuit the greatest wattage will develop where the resistance ishighest. It is thus possible to provide a heater in which the Vheatvaries in longitudinal strips or in lateral bands or in both strips andbands. When heater Wires are used for both the Warp and the Woof, We ft.

may connect the warp and Woof circuits in series or in parallel or eachmay be connected to operate independently of the other. Thermostaticmeans may be provided to control the operation of either circuit.

To give mechanical strength and dielectric protection the heater fabricmay be impregnated with rubber, silicone, resin or other flexiblebind..- er. Where' additional protection or a smooth surface isrequired, We may encase the heater in a sheath of rubber or othersuitable material such as neoprene. The sheath may be moulded orvulcanized directly to the heater or it maybe removable.

These and other features and objects of our invention will appear fromthe following description thereof in which reference is made to theaccompanying figures of the drawings.

In the drawings- Figure 1 is a side elevation of a propeller bladeembodying a form of our invention;

Figure 2 is an enlarged cross sectional View of the leading edge of asurface carrying one of our de-icers;

Figure 3 is a cross sectional enlarged nview of one of the de-icers;

Figure 4 is a view of the heating element;

Figure 5 is a schematic view of a series of elements adapted to bepositioned Within one cover;

Figure 6 is another View of a heating element Woven in the form of aflexible fabric; l

Figures 7 to 11 inclusive are wiring diagrams.

Referring more particularly to the drawings, Figure 4 discloses aheating element I'U made up of Warpwires Il and Woof members l2. Thewarp is made of flexible resistor Wires while the Woof is Woven ofthread made of glass, asbestos, yor other heat resisting vdielectricmaterial. The length of unit l0 depends upon the area to be covered and,in the case of the propeller blade, this would be determined by thelength ofthe blade. As the unit is woven and completeda copper elementl5 is woven into the fabric ad- 'jacent the end of the unit to form twostrands I6 and I'l. It will be noticed that the strand I6 passes underthe copper Wires which the strand I1 passes over so that each wire iscontacted on both sides by the copper element. This element may then besoldered to the warp wires Il and then cut in sections to form separateconnection members, as illustrated in Figure 6. The type of cuttingmembers shown in Figure 6 are slightly different but the effect ofcutting the copper element I5 is the same. For strength and to form aproper edge 22 the glass fibers 23 may be used as warp threads ratherthan the resistor wires. It will be understood that lead wires 24 and25, as shown in Figure 1, will be connected to the element similarto thelead 55 shown in Figure 6. v v

y In making thegunit the copper element 'l5 is cut so that theconnecting element in the center of the unit connects fewer ywires thanthose` at the outer edge. This resultsV in increased heating in thecentral zones and of varying watt density per square inch.

The heating element l is preferably engaged in a suitable cover 3U whichis `feathered at 3l for smooth installation. It has been found that theheating element l0 may :be readily encased in uncured neoprene which maythen be cured and fused about the heating element to form a flexiblecovering which may be cemented on the leading edge of the plane wing orlon the leading edge of a propeller blade, as shown in Figure 2. If thearea to be heated is such that the continuous heat of the entire surfacewill overtax the capacity of the generator furnishing the current thearea may be divided into zones, each supplied by a Separate heatingelement, as Shown in Figure 5. There the area 35 is divided into zonesby separate heating elements 36, 31, 38 and 39 having separate leads 4t.By any conventional means the current may be alternately or successivelyfed to selected zones. Similarly a 4fourblade propeller having a unit oneach blade may be heated by successively feeding the current for apredetermined time, thus using a minimum amount of current to :preventthe formation of ice.

Referring to Figure 6, this particular unit 50 is made up with a warpcomposed of 60 heater wires 5I of equal resistance and eight glassthreads 52. The Woof 53 is a glass thread. The warp wires are connectedin series of groups by connectors 54 made of flexible braided coppertabs. The numerical grouping of the sixty wires is as follows-9-8-7-6-6-'7-8-9. The amount lof heat emitted per unit of surface willbe greatest in the central longitudinal strip covered by the six wiregroups and the heat will decrease in three successive steps toward eachedge. The entire circuit is connected to a source of electric power bylead wires 55.

It will be appreciated that the ends of each adjacent group at one endof the unit are connected by one yof the connectors 54.

Figure 7 is a simplified diagram of the type of circuit shown in Figure6. The twelve equal resistance wires VI, VII and VIII are arranged inserially connected groups having the numerical 'ratio 3, 2, I-l, 2, 3.The greatest amo-unt of heat is emitted by wires VIII, lless is emittedby Wires VII and least by Wires VI.

In Figure 8 the modification of circuit shown in Figures 6 and 7 isshown. The wires IX and X are serially connected in groups of 2-2-2 withwires X having greater resistance than wires IX.

With this arrangement more heat is emitted by the two center strips thanby the two outer strips.

In Figure 9 is shown a heater composed of equal resistors in which theheat decreases from the center to the edges and valso from the bottom tothe top. Thus a section through the line B-B will emit more heat than asection through the line A-A.

Figure 10 is a modication of the circuit shown in Figure 9. The wiresXVII have the greatest resistance, wires XVI have less and wires XV theleast resistance. Here again the heat will decrease fromzthe center tothe edges and from the bottom to the top. A section through the line D-Dwill be hotter than a section through the line C-C.

In Figure 11 a diagram of a heater is shown in 'which the Woof 56 formsone `or more electric heater circuits woven through but insulated fromthe warp 51. The warp circuits may consist of any combination ofresistors including the arrangements shown in Figures 1 5. The warp andWoof circuits may be connected in series, in parallel or they maybeseparated by separate controls.

It will be understood that the foregoing are merely examples of theapplication of our invention and Iare typical of the embodiments whichmay 'be employed. However, numerous changes and modications may be madein the form and the .arrangement of parts without departing from thespirit of the invention and it should be understood that we do notintend the invention to be limited to the illustrative embodiments setforth.

We claim:

1. A flexible heating element for heating the leading edge of an airfoil, said element comprising a woven fabric, the warp of said fabricrunning parallel to said airfoil edge and consisting of a plurality ofresistor wires and the Woof of heat resisting dielectric material,electrical conducting elements woven into said heating element, saidconducting elements contacting and connecting certain of said resistorwires in mechanically and electrically parallel groups and connectingsaid groups electrically in series whereby the heat intensity developedin said groups will vary in inverse proportion to the number of wires ineach group.

2. A flexible heating element for heating the leading edge of `an airIfoil, said element comprising a woven falbric, the warp of said fabricrunning parallel to said air foil edge and consisting of a plurality ofresistor wires and the Woof of heat resisting dielectric material,electrical conducting elements woven into said heating element, saidconducting elements contacting and connecting certain of said resistorwires in mechanically and electrically parallel groups and connectingsaid groups electrically in series whereby the heat `producing area ofthe greatest intensity is in closest proximity to the edge of the airfoil paralleling the same, the second heat producing area ofintermediate intensity is spaced from the first and the third heatproducing area of least intensity is spaced from the second area.

3. A flexible heating element for heating the leading edge of anairfoil, said element comprising a woven fabric encased in a protectivecovering, the warp of said fabric running parallel to said airfoil edgeand yconsisting of a plurality of resistor wires, and the Woofconsisting of heat resisting dielectric material, said resistor wiresbeing grouped with the ends yof each group being connected and with eachgroup connected t0 the adjacent group, a conducting element connected toeach of the outside groups whereby the heat intensity developed in saidgroups will vary in inverse proportion to the number .of wires in eachgroup.

ROBERT S. ELY. IRVING M. KETCHAM.

REFERENCES CIIED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Rideau et al June 25, 1940

